Following an investigation, Siemens says two separate incidents in which a B53 rotor blade broke off were both caused by "adhesive bonding failure." The blades are 53 meters long and used primarily on SWT-2.3-108 turbines in the U.S.

In April, a Siemens service technician discovered a B53 blade on the ground at the Eclipse wind farm. The 200.1 MW project, located in Iowa, features 87 SWT-2.3-108 turbines and is owned by MidAmerican Energy Co.

Another B53 blade then broke off at Pattern Energy’s Ocotillo Wind project in May. The 265 MW facility features 112 SWT-2.3-108 turbines and is in California’s Imperial Valley.

Following the incidents, Siemens launched a root-cause analysis and announced it was curtailing all turbines with the B53 blade type globally. Now that the investigation has ended, a Siemens spokesperson says the blade failures were “not related to the design of the blade.”

“Siemens concluded that the fractures happened as a result of adhesive bonding failure between pre-cast root segments and the fiberglass laminate of the main blade," the spokesperson says. “Root segments are pre-cast inserts used to construct the blade root and are supplied to Siemens by a number of suppliers. The adhesive bonding failure was caused by insufficient surface preparation of the root segments.”

All existing B53 blades have been inspected, and most turbines with the blade type have returned to operation. However, the spokesperson says Siemens will replace a certain number of blades after discovering indications of delamination.

“As a precautionary measure, Siemens will apply a minor modification in the field to all existing B53 blades worldwide that are not otherwise replaced,” the spokesperson continues. “This upgrade will provide an extra level of protection through an incremental enhancement of the bond between pre-cast root and the fiberglass laminate.”

All wind turbines at MidAmerican’s Eclipse farm are up and running. Pattern Energy ceased operation at Ocotillo following the blade incident, but a company spokesperson has confirmed that Pattern is beginning to bring the project’s turbines back online one at a time. The spokesperson says work will continue at least through the end of this month.

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